The present research project is related to the influence of plasma and cardiac renin-angiotensin system on the regulation of cell communication in the heart. My major aim is to understand the role of the cardiac renin- angiotensin system on the process of gap junction communication as well as on impulse propagation. Heart cell pairs will be obtained by enzymatic dispersion of adult rat or hamster ventricle. To determine the junctional conductance two isolated voltage clamp systems will be used. Giga-ohm scaling will be obtained and then th cell membrane of both cells of the pair will be broken by stronger suction. The holding potential of both cells will be .40 mV. Cell 1 will be then pulsed to O mV while membrane potential of cell 2 will be kept unchanges. The junctional resistance (or conductance) will be then determined with values of junctional current and transjunctional voltage. Action potentials will be recorded from intact papillary muscles or Parkinje fiber with intracellular electrodes. It is known that the cardiac renin-angiotensin system is activated during congestive heart failure or myocardial infarction but the real meaning of this phenomenon is not known. The present research project is involved with the study of this problem and will certainly provide important information on the role of this system on cell communication.